Contractor discussions, DIY tasks and Derate Factors

Well, we met our Solar contractor today and yeah…. he’s a geek right down to the Nikola Tesla is his hero part. More importantly, we’re both on the same page concerning the installation. He has no problems letting me save $$$ by doing parts of the job myself so I’ll probably do the array mounting rails up on the garage roof, run the electrical conduit from the panels to the meter base and help install the panels themselves. Working in a hot attic is no fun but if the weather stays cool the attic won’t get too bad. I’ll just run a big cooling fan or do it at night if it does.

I’ve decided on our panel manufacturer too. I’m purchasing high performance mono crystalline 60 cell panels from Sunivia, a company located in Norcross GA. These guys use high-tech automation to manufacture some of the most efficient panels on the market and, because its all automated, their prices are great too. I’m going with their OPT270 line which are 270 watt, 60 cell panels that cost $320 each delivered. The increased wattage will drive the enphase micro inverters better in low-light/shaded situations too. Since each inverter produces 218 watts, the initial 4 panel array will then be capable of producing 872Watts @ 240VAC from a combined 1080W DC input. This difference is known as the “derate factor” and is based on inverter efficiency, wire coupling losses, and resistance.

I’ll be purchasing the panels/inverters/mounting hardware directly and my contractor will guide/inspect any work that I do and also handle the main electrical hookup work. That includes installing the double meter base and pulling wire through the conduit that I run. He will also pull permits and help out with WE energies paperwork if I get stuck.

He’s going to get me an estimate next week with DIY options laid out. He will also do a quick Solar Pathway analysis of the site to see if he can validate my numbers which ended up being a bit high at 20.54%. Since his software can account for the varying shade factor of deciduous trees, it’s likely that he can hit a better number than I did however. Still, I’ll be quite surprised if he tweaks it below 10% to qualify me for the WI focus on Energy subsidy…

Speaking of Solar surveys, here’s my final analysis which I verified by actually watching the shading factor on the roof at sunrise/sunset:

The times shown are CST. The 20 degree shade area at the left are two silver maples in the side yard and the similar area on the right are two red maples in the other side yard. I actually took elevation readings every 10 degrees from 60 – 320 then inputted the data into Solar Shading, a cool Android app that did the shading calculations. At $14 its a bit steep but it does produce a very nice report showing not only a graph like the one above, but also several bar graphs showing shading factor/power output by month. It thinks we have a 20.54% shading factor but only a 5% power loss factor since the main shading areas occur in the morning and evening hours when the array isn’t producing much power anyway.

Stay tuned; I’ll be chatting about my options next week when I get my job estimate back. I’m pumped to get this done before the Solar Solstice